This invention relates to methods for casting cylinder heads for internal combustion engines, and more particularly to methods of assembling core elements of core assemblies.
The manufacture of cylinder heads for internal combustion engines poses difficult manufacturing problems. The cylinder head of an internal combustion engine, whether for a spark driven gasoline internal combustion engine or a compression ignition diesel engine, is a complex article of manufacture with many requirements. A cylinder head generally closes the engine cylinders and contains the many fuel explosions that drive the internal combustion engine, provides separate passageways for the air intake to the cylinders for the engine exhaust, carries the multiplicity of valves needed to control the air intake and engine exhaust, provides a separate passageway for coolant to remove heat from the cylinder head, and can provide separate passageways for fuel injectors and the means to operate fuel injectors.
The walls forming the complex passageways and cavities of a cylinder head must withstand the extreme internal pressures, temperatures and temperature variations generated by the operation of an internal combustion engine, and must be particularly strong in compression-ignition diesel engines. On the other hand, it is desirable that the internal walls of the cylinder head, particularly those walls between coolant passageways and the cylinder closures, permit the effective transfer of heat from the cylinder head, and it is also important that the cylinder head include minimal metal to reduce its weight and cost.
These countervailing requirements make the manufacture of reliable cylinder heads difficult. Furthermore, these complex parts are manufactured by the thousands and assembled into vehicles that must operate reliably under a variety of conditions. The manufacture of reliable cylinder heads is particularly important because of the high cost of their replacement. Consequently, the manufacture of cylinder heads has been the subject of the developmental efforts of engine and automobile manufacturers throughout the world for years.
Cylinder heads are most generally manufactured by casting them from iron alloys. The casting of the cylinder head portion that closes the cylinders, carries the intake and exhaust valves and fuel injectors and provides the passageways for the air intake, exhaust and coolant requires a mold carrying a plurality of core elements. To provide effective cooling of the cylinder head and effective air intake and exhaust from the cylinders of the internal combustion engine, the passageways for the air intake and exhaust are best interlaced with the coolant passageways within the cylinder head portion. The cavities for coolant, air intake and exhaust must, of course, be formed by core elements within the mold that can be removed when the casting metal solidifies.
Such core elements are formed from a mixture of core sand and a curable resin, which, when cured, retains the shape imposed on it prior to curing, and after a casting solidifies, the core sand and resin residue are removed from the casting.
As a result of recent developments, core assemblies are provided by a plurality of core elements that have interengaging surfaces to locate the plural core elements in the core assembly. For example, head core assemblies can be formed by the assembly of a one-piece coolant jacket core, a one-piece exhaust core, and a one-piece air intake core that interengage during their assembly; however, to maintain such an assembly together as a unit during post assembly handling and casting, the core elements must be fastened together. In the past, adhesive and/or screws have been used to fasten at least two core elements together to maintain the integrity of the core assembly during its handling and during pouring of the casting.
The use of an adhesive requires an adhesive that can be easily spread on the core elements, that will set within the shortest possible time; that will hold the core elements together as one piece and maintain their position during the casting process, and that may be removed from the casting after the casting metal solidifies. This method results in substantial costs and opportunities for unreliable castings because of a potentially unreliable interface between the core elements. It is necessary that workmen apply the adhesive correctly so that the adhesive reliably maintains the core elements together during casting. Furthermore, this method requires time for applying the adhesive, assembling the core elements together and allowing the adhesive to set before the core elements can be used for casting, and it introduces into the mold an unnecessary foreign element in the form of an adhesive that may evolve gas that may become trapped in the solidified casting and cause areas of possible failure.
Because of the difficulties of using adhesive to fasten core elements together, the use of screws to fasten together the core elements of core assemblies has been preferred. Although the use of screws to fasten core elements together provides a more predicable assembly of the core elements, it can introduce screws into the casting, which may not be removed after the casting has solidified and may cause failure of an assembled engine.
The invention provides a method of fastening assembled core elements together without the use of foreign agencies, such as adhesives, screws or other such fasteners, using instead the same core sand and resin that form the core elements themselves.
In the invention, core sand elements are retained in an assembly by a body of cured core sand and resin that spans the interface between the core elements and fastens the core sand elements together. The core sand elements are fastened together by providing the core sand elements with alignable holes, or cavities, inserting a mixture of core sand and a curable resin, preferably the same resin used in forming the core sand elements, into the holes or cavities of the core elements to provide a body of uncured core sand/resin in the holes, or cavities, and at the interface, and curing the curable resin to provide a body of cured core sand and resin, preferably adhering to the core sand elements, fastening the core sand elements together. In a preferred method of the invention, holes are drilled in the assembly elements after they are assembled and a fluent mixture of core sand and uncured resin is compacted into the drilled holes to provide improved adhesion between the cured core sand/resin fastening elements and the hole surfaces of the assembled core elements.
Other steps, features and advantages of the invention will be apparent to those skilled in the art from the drawings and more detailed description of the best known mode of the invention that follows.
FIG. 1 is a cross-section of the core elements that have been fastened together in an assembly with the method of this invention.
FIGS. 2A-2D diagrammatically illustrate a preferred method of the invention.
FIG. 3 illustrates, as an example, head core elements that can be fastened together with the invention.
FIG. 4 illustrates the head core assembly of FIG. 3 as fastened together with the invention.
FIG. 5 diagrammatically illustrates the fastened head core assembly of FIG. 4 being assembled with a green sand mold.
FIG. 6 diagrammatically illustrates the fastened head core assembly and green sand mold ready for casting.
FIG. 7 diagrammatically illustrates core elements with preformed cavities providing interlocking engagement in an assembly of the invention.